This invention relates generally to voltage regulation in electric power systems and, more particularly, to electric power systems which compensate for voltage drops in power conductors.
Constant speed drive electrical power systems which are typically found on commercial aircraft, couple an electric generator to the aircraft engine through a hydromechanical transmission which drives the generator at a constant speed to produce constant frequency output voltage. Variable speed constant frequency (VSCF) power systems include a generator which is directly coupled to the engine and therefore driven at variable speeds. The variable frequency output of this generator is electronically converted to a constant frequency output. It is desirable to retrofit existing constant speed drive equipped aircraft with variable speed constant frequency power systems. A key to successful retrofit lies in the design of a VSCF system which is directly interchangeable with the existing CSD system. This precludes aircraft wiring changes or changes in any of the other system components. To accomplish this objective, the VSCF converter and its controls must be in the same package as the generator.
The VSCF converter and associated controls would be mounted adjacent to the aircraft engine. A multiple phase power bus connects the engine mounted VSCF system to the aircraft loads. The VSCF voltage regulator senses the voltage at the output terminals of the VSCF system. Thus, the voltage received at the load end of the power bus is dependent upon load current and feeder impedance. This results in unsatisfactory voltage regulation at the load terminals.
One approach which has been used to compensate for line voltage drop is to develop a signal proportional to load current which is injected into the VSCF voltage regulation loop. This approach is unsatisfactory for aircraft systems because it is dependent upon feeder length, changes in feeder impedance because of temperature extremes, and changes in impedance because of feeder spacing from each other and the skin of the aircraft. Furthermore, the feeder voltage drop is dependent upon the power factor of the load.
It is therefore desirable to devise an electric power system having line drop compensation which is independent of feeder length, feeder impedance, load current and power factor.